U.S. Pat. No. 4,674,834 of George D. Margolin, issued June 23, 1987 and assigned to the assignee of the present invention discloses a document scanner including a fiber optic subassembly. The fiber optic bundle in the disclosed scanner is non-coherent. That is to say, there is no known relationship between the positions of two ends of any particular fiber in their respective fields.
To obtain the positional correspondence between the two ends of a fiber, the patent calls for attaching an array of discrete sensors to the exit field of the bundle and noting the address of any illuminated sensor in the array when light is directed into an end of a fiber in the entrance field. By sending light into a fiber in the entrance field, we, so to speak, are asking each fiber where its exit end is positioned.
The initializing procedure is easy to visualize but cannot actually be carried out as described. The reason for this is that the fiber ends in the entrance field are very tiny--many thousands over the widthg of an 81/2 inch document. Therefore, the fibers are only a fraction of the size of a human hair. Moreover, the fiber ends move, during production, from their ideal positions. The actual position of the fiber ends in the entrance field is not known. For a document scanner which requires an ideally linear entrance field, the fiber ends are displaced laterally from the axis of the line, are unevenly spaced along the axis and frequently bunch up. Not only is the position of each fiber unknown, but even if it were known, the apparatus to move a beam to the known position would be too costly to use.
The above-mentioned patent discloses a technique for moving a slit along the axis of the entrance field. The slit has a width small compared to the diameter of a fiber and is moved in increments small compared to that diameter. For an entrance field of 81/2 inches, the slit is moved in 10,000 increments, for example. The sensor array is interrogated 10,000 times, one for each increment. The addresses of the illuminated sensors are recorded during each interrogation.
Each fiber has a diameter large compared to the size of a sensor in the array. Thus, each fiber corresponds to about twelve sensors. This relationship of many sensors to each fiber permits the use of defective sensor arrays as well as the opportunity to choose sensors of like sensitivities. Typically, at least one sensor is chosen each time the initializing beam is incremented and the sensor array is interrogated. The initializing procedure thus can be seen to result in the initialization of space rather than fibers relating beam position to sensor address. It should be clearly understood that the sequence of sensor addresses is obtained for the sequence of slit positions not necessarily for the sequence of fiber ends in the entrance field. The initializing procedure results in the organization of pixels (picture elements) of the exit field of a fiber optic bundle to correspond to the organization of pixels in the entrance face of that bundle as disclosed fully in my above-mentioned patent.
The present invention addresses the problem of how one initializes large numbers of fiber optic subassemblies in production.